Generally, coating systems which are currently in use for coating vehicle bodies or the like, are largely constituted by a working mechanism which is provided with a swinging arm, a coating machine which is mounted on a fore end portion of the arm, and a paint hose which supplies paint to the coating machine. The upstream end of the paint hose is connected to a color changing valve assembly which is arranged to supply a selected paint color from paint sources of different colors.
In the case of coating systems of this sort, however, it becomes necessary to supply solvent and thereby washing away paint residues from the paint hose, and to discharge spent solvent from the machine each time when changing the paint color. Therefore, each color change not only entails wasteful consumption of paint and solvent but also takes an objectionably long period of time.
In this regard, attempts have been made to mount a color changing valve assembly on an arm of a working mechanism for the purpose of shortening the length of a paint hose between the color changing valve and a coating machine, as proposed in Japanese Patent Publication No. S62-20853. A coating system of this sort, however, has an inherent problem that the performance quality of a working mechanism is deteriorated to a considerable degree due to an increased weight which is put on the arm of the working mechanism and a large number of hoses which are connected to a color changing valve assembly to impede operations of the arm.
As a second prior art coating system which is free from the problems just mentioned, there has been known a coating system (e.g., Japanese Laid-Open Patent Publication No. S63-175662) employing a coating machine which is adapted to be mounted on a fore end portion of an arm and provided with a paint tank, the content of which is replaced each time when changing the paint color. Consequently, the second prior art coating system succeeded in abolishing the color changing valve assembly and in reducing the number of hoses.
Further, as a third prior art coating system, it has been known to provide a large number of paint cartridges which are filled with paint of different colors, which are adapted to be selectively and replaceably mounted on a housing of the coating system (e.g., Japanese Laid-Open Patent Publication No. H8-229446).
In the case of the above-mentioned second prior art coating system (Japanese Laid-Open Patent Publication No. S63-175662), a paint tank which is provided on a coating machine has to be washed on each color change and before filling a new color thereinto. Therefore, a problem with this coating system is that a color changing operation takes a great deal of time.
Besides, in the second prior art coating system, an air hose which supplies air to the coating machine for spraying paint is usually allowed to hang down from the arm of the working mechanism. This air hose could cause coating defects by contacting a coating surface of a work piece during a coating operation or could be damaged contact with other moving parts of the machine.
Further, in the case of the third prior art coating system (Japanese Laid-Open Patent Publication No. H8-229446) employing paint cartridges for different paint colors, it becomes necessary to provide a paint charging device in the vicinity of the coating system for charging or filling paint into a dismantled cartridge each time when changing the paint color although such a paint charging operation is troublesome and takes time.